This invention relates to intrusion sensors, and particularly to passive infrared intrusion sensors which make use of a focusing lens for focusing self-emitted infrared radiation from an intruder onto an infrared radiation detector for purposes of sensing the presence of the intruder.
In connection with passive infrared intrusion sensors, it is generally desirable to make the sensor as unobstrusive as possible to an intruder, so that an intruder cannot easily avoid passing into a zone of detection of the intrusion sensor by observation of the device itself as installed on a protected premises. One approach to making such devices less noticeable to a casual intruder is to make the devices as small as possible.
It is an object of the present invention to provide a passive infrared intrusion sensor which is compact compared to similar devices known in the prior art.